The present invention relates to an improved polypropylene filter media separator for battery plates and to batteries containing the same.
Battery plates for industrial or automotive storage batteries of the lead acid type are conventionally manufactured by casting a grid structure in a mold. The grid usually comprises a rectangular frame formed with openings, and a laterally projecting conductive lug on its periphery by means of which a plurality of grids of similar polarity may be fused together or otherwise electrically connected in parallel as by a bar leading to a battery post. The grid is coated with an active material paste of lead oxide containing some sulphuric acid, whereafter it is heated to dry and somewhat solidify the paste. The resulting structures, called battery plates, are then subjected to an electrical charge while in sulphuric acid, whereby one group of plates called the negative plates have their lead oxide converted to lead, and another group of plates called the positive plates have their lead oxide converted to lead dioxide.
To prevent shedding of the active material coating from the battery plates when the same are used in a battery, each plate is wrapped or encased in a separator material which ideally on the one hand securely retains the coating on the plate, while on the other hand allows unimpeded electrochemical action of the plate when formed with one or more additional plates into a battery. Conventionally, each plate is wrapped in a separator material which is usually of fiberglass. To this end, a fiberglass mat is folded around the plate, and to hold the mat in position on and against the plate a plastic "foot" or sheet of material is folded around the bottom of the plate and mat, and an overlay sheet of perforated plastic is folded around the mat and foot lengthwise of the plate. Ends of the outer sheet of plastic material are then overlapped and joined, for example by heat sealing, to complete the assembly. The wrapping process is a manual operation, and is quite undesirable since fiberglass is a relatively hazardous material to handle and work with.
A series of wrapped plates is then placed in a cell with alternating negative and positive plates and a separator, which may be of fluted wood, perforated rubber, cork, plastic material or the like, is positioned between adjacent pairs of plates. The cell may comprise any number of plates, with the positive plates being connected in parallel and the negative plates being connected in parallel, so that the entire cell has a desired amperage rating. A requisite number of cells are then inserted into a container which forms the outer housing of the battery, the cells are connected in series, a cover is installed on the container and electrolyte is introduced therein to complete the battery.
Manifestly, battery plate assemblies and the resulting batteries of the type described are not only difficult, time consuming and tedious to construct, but also present a serious hazard to health because of the required manual handling of the fiberglass separator material. In addition, the plate assemblies have a significant overall thickness comprised of the combined thicknesses of the battery plates themselves, the fiberglass mat, the plastic foot, the outer plastic wrapping sheet, and the individual separators placed between adjacent pairs of plate assemblies, which severely limits the number of plates that may be packaged in a battery of given size, and therefore the capacity of the battery.